Long Term Evolution/Evolved Packet Core (LTE/EPC) is standardized by 3GPP as a next-generation mobile communication system following the third generation mobile telephone network (3G mobile system). LTE/EPC includes an LTE network (a wireless access network conforming to LTE, referred to as eUTRAN) and an EPC network (also referred to as System Architecture Evolution (SAE)) as a core network. The EPC network is connected via an IP multimedia subsystem (IMS) network to an Internet protocol (IP) network (packet network). The IP network is an Internet service provider (ISP) network (Internet) or an intranet, for example.
A mobile station (mobile terminal, referred to as user equipment (UE)) can connect to the EPC network via the LTE network acting as a mobile network, for example, and is connected to the IP network via the EPC network and the IMS network. A mobile terminal can access various servers and terminal apparatuses connected to the IP network to receive various packet communication services (e.g., web services, Voice over IP (VoIP), and IPTV broadcasting).
The EPC network has multiple nodes such as mobility management entity (MME), serving gateway (S-GW), packet data network gateway (P-GW), and policy and charging rule function (PCRF). A mobile terminal is connected via S-GW and P-GW to the IMS network, enabling access to the IP network.
A mobile terminal performs communication using a communication line set based on a bearer in the mobile network. During movement of the mobile terminal, a handover function between transmitting apparatuses (S-GW, P-GW) in the mobile network enables a predetermined communication service to be continued without interruption of the communication.
Communication services include IPTV broadcasting and IP radio broadcasting, in which multicast packets are transmitted to multiple mobile terminals participating in viewing. A technique is disclosed for continuing communication in a multicast service such as IPTV broadcasting during movement of a mobile terminal. For example, a relay apparatus is disposed in the IP network and connected through a logical tunnel so as to deliver unicast data via the tunnel while multicast data is relayed by a multicast delivery network and delivered to users without going through the tunnel. In another technique, a multicast delivery proxy apparatus in a public network converts a destination address into a multicast address to perform broadcast delivery to users without using a relay apparatus. In yet another technique, in response to “position information registration” from a mobile terminal, a viewing state for the mobile terminal is changed in a handover-source apparatus and a handover-destination apparatus. In a further technique, in response to detection of a handover condition by a mobile terminal, the mobile terminal sets a line for multicast reception addressed to an off-load apparatus in the vicinity of a handover-destination base station (eNB) and, via this line, the mobile terminal participates in multicast viewing (see, for example, Japanese Laid-Open Patent Publication Nos. 2002-374276, 2001-177564, and 2007-228450).
In a configuration with a transmitting apparatus (P-GW) delivering IPTV broadcasting to mobile terminals through a communication line for viewing, the IPTV broadcast can continuously be viewed without interruption during movement of a mobile terminal. However, in this technique, respective communication lines are set for mobile terminals from the transmitting apparatus (P-GW) to a base station (eNB) and multicast packets are transmitted to each of the communication lines. This is the same even when the same IPTV broadcast is viewed by multiple mobile terminals, increasing traffic of an EPC network. Particularly, as the number of mobile terminals increases, the traffic significantly increases. For example, if ten mobile terminals are present, even when multicast packets have the same contents, ten communication lines are necessary from P-GW to the mobile terminals and the traffic carrying the same contents must go through each of the ten communication lines at the same time (see, e.g., Japanese Laid-Open Patent Publication No. 2002-374276).
In a configuration changing a mobile terminal viewing state a at a handover-source apparatus and a handover-destination apparatus, the position registration of the mobile terminal is performed after the mobile terminal completes a handover process and therefore, the multicast packet communication is interrupted at the time of handover, causing a problem of interruption in delivery of IPTV broadcasting (see, e.g., Japanese Laid-Open Patent Publication No. 2001-177564).
On the other hand, in the technique in which in response to detection of a handover condition by a mobile terminal, the mobile terminal sets a line for multicast reception addressed to an off-load apparatus in the vicinity of a handover-destination base station (eNB), the IPTV broadcast can continuously be viewed without interruption during movement of the mobile terminal. However, in this technique, a new respective communication lines are set for mobile terminals from the transmitting apparatus (P-GW) in the vicinity of a destination to the base station (eNB) and transmission for participating in multicast viewing is performed through each of the new communication lines. This is the same even when the same IPTV broadcast is viewed with multiple mobile terminals, increasing traffic of a wireless section network. Particularly, as the number of moving mobile terminals increases, the traffic of the wireless section network significantly increases. For example, even when multicast packets have the same contents, ten mobile terminals require reestablishment and participation in viewing of ten new communication lines from P-GW in the vicinity of a destination to the mobile terminals. Additionally, a communication line to a transmission device (P-GW) in the vicinity of an original location must be disconnected (see, e.g., Japanese Laid-Open Patent Publication No. 2007-228450).
As described above, when a multicast service is executed for mobile terminals, conventional techniques cannot achieve both continuous viewing during movement of a mobile terminal and suppression of traffic increases in the EPC network.